Stress-Induced Anisotropy in Magnetic Memory Cells
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Solution Overview
Problem
Current nonvolatile solid-state data storage devices, such as flash memory, face challenges like slow access speed, limited endurance, and integration difficulties, while magnetic random access memory (MRAM) experiences scaling issues due to increased switching magnetic field variation as magnetic tunnel junction size shrinks.
Innovation Solution
The development of magnetic memory cells with stress-induced magnetic anisotropy, achieved by combining specific materials for the bottom electrode and memory element, including ferromagnetic layers and a non-magnetic spacer layer, to enhance thermal stability and reduce write current, while also improving robustness against defects caused by process imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If magnetic tunnel junction size is shrunk to reduce device area, then device integration density is improved, but switching magnetic field variation increases and switching becomes less reliable
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from perpendicular magnetization to in-plane magnetization by applying stress to the ferromagnetic layer. This parameter change allows the magnetic moment to align along the stress direction, providing stable switching behavior even at reduced device dimensions where perpendicular magnetization would exhibit high variation.
Solution Approach 2:
The patent employs a composite structure consisting of a ferromagnetic layer combined with a stress-applying layer (such as silicon nitride or silicon oxide). This composite material system generates stress-induced magnetic anisotropy that stabilizes the magnetic switching process, enabling reliable operation at smaller device areas.
2Length of moving object
If ferromagnetic layer thickness is reduced to improve scaling, then device size is decreased, but thermal stability deteriorates
Solution Approach 1:
The patent changes the magnetic anisotropy energy parameter by introducing stress-induced anisotropy. This modifies the energy barrier for magnetic switching, allowing thinner ferromagnetic layers to maintain adequate thermal stability through the stress-generated anisotropy field rather than relying solely on perpendicular magnetization from thick layers.
Solution Approach 2:
The stress is applied to the ferromagnetic layer during or after deposition to establish the desired in-plane magnetic anisotropy before the layer is used for memory operations. This preliminary stress application ensures that the magnetic properties are optimized for thermal stability at reduced thicknesses.
3Reliability
If stress is applied to induce in-plane magnetic anisotropy, then switching field variation is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent uses composite material systems where a stress-generating layer (such as silicon nitride, silicon oxide, or tungsten) is combined with the ferromagnetic layer. These materials naturally generate the required stress through their intrinsic properties or thermal expansion differences, eliminating the need for complex external stress application equipment while achieving consistent in-plane magnetic anisotropy.
Solution Approach 2:
The stress is applied locally to the ferromagnetic layer through the stress-generating layer, creating the desired in-plane magnetic anisotropy only where needed in the memory device. This localized approach allows standard manufacturing techniques to be used without requiring global process modifications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides enhanced thermal stability, reduced write current, and improved robustness against defects, leading to more reliable and efficient magnetic memory cells with stress-induced anisotropy, which addresses the scaling issues and performance limitations of existing technologies.
Implementation Method 1
The magnetic memory element has a stress-induced magnetic anisotropy, a result of the combinations of materials of the bottom electrode and memory element
Implementation Method 2
The free layer formed of a material with magnetostriction
Data Source
AI summary
A magnetic memory element that has a stress-induced magnetic anisotropy. The memory element has a ferromagnetic free layer having a switchable magnetization orientation switchable, a ferromagnetic reference layer having a pinned magnetization orientation, and a non-magnetic spacer layer therebetween. The free layer may be circular, essentially circular or nearly circular.